A new method utilizing a radioimmunoassay for plasma and androgens has been devised requiring very small amounts of blood. This new method makes studies of newborn infants feasible. The following androgens can be determined with accuracy and precision: testosterone, dihydrotestosterone, delta 4-androstenedione, and dehydroepiandrosterone. This method has been utilized to study ovarian virilism, androgens of adrenarche, ambiguous sexual development, hypertension in city high school students, androgens in adolescent heroin addicts in a methadone detoxification program. An extensive investigation of the mechanism of childhood hypertension in two forms of adrenal hypertension has been carried out. An investigation into the etiology of hypertension was carried out in 28 New York City high school students found to be hypertensive in a high school screening program.